calculate end effector path length in moveit

I need to find the path which is traveled by end_effector that is called path length in moveit. i have used planning interface but It is difficult to get path length because MotionPlanResponse does not provide this output. (http://docs.ros.org/jade/api/moveit_core/html/structplanning__interface_1_1MotionPlanResponse.html) could anyone please advise me or give me sample code if it is already available. thanks